'\" t
.TH "SYSTEMD\-TIMESYNCD\&.SERVICE" "8" "" "systemd 255" "systemd-timesyncd.service"
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.SH "NAME"
systemd-timesyncd.service, systemd-timesyncd \- Network Time Synchronization
.SH "SYNOPSIS"
.PP
systemd\-timesyncd\&.service
.PP
/usr/lib/systemd/systemd\-timesyncd
.SH "DESCRIPTION"
.PP
systemd\-timesyncd
is a system service that may be used to synchronize the local system clock with a remote Network Time Protocol (NTP) server\&. It also saves the local time to disk every time the clock has been synchronized and uses this to possibly advance the system realtime clock on subsequent reboots to ensure it (roughly) monotonically advances even if the system lacks a battery\-buffered RTC chip\&.
.PP
The
systemd\-timesyncd
service implements SNTP only\&. This minimalistic service will step the system clock for large offsets or slowly adjust it for smaller deltas\&. Complex use cases that require full NTP support (and where SNTP is not sufficient) are not covered by
systemd\-timesyncd\&.
.PP
The NTP servers contacted are determined from the global settings in
\fBtimesyncd.conf\fR(5), the per\-link static settings in
\&.network
files, and the per\-link dynamic settings received over DHCP\&. See
\fBsystemd.network\fR(5)
for further details\&.
.PP
\fBtimedatectl\fR(1)\*(Aqs
\fBset\-ntp\fR
command may be used to enable and start, or disable and stop this service\&.
.PP
\fBtimedatectl\fR(1)\*(Aqs
\fBtimesync\-status\fR
or
\fBshow\-timesync\fR
command can be used to show the current status of this service\&.
.PP
systemd\-timesyncd
initialization delays the start of units that are ordered after
time\-set\&.target
(see
\fBsystemd.special\fR(7)
for details) until the local time has been updated from
/var/lib/systemd/timesync/clock
(see below) in order to make it roughly monotonic\&. It does not delay other units until synchronization with an accurate reference time sources has been reached\&. Use
\fBsystemd-time-wait-sync.service\fR(8)
to achieve that, which will delay start of units that are ordered after
time\-sync\&.target
until synchronization to an accurate reference clock is reached\&.
.SH "FILES"
.PP
/var/lib/systemd/timesync/clock
.RS 4
The modification time ("mtime") of this file is updated on each successful NTP synchronization or after each
\fISaveIntervalSec=\fR
time interval, as specified in
\fBtimesyncd.conf\fR(5)\&.
.sp
When initializing, the local clock is advanced to the modification time of this file (if the file timestamp is in the past this adjustment is not made)\&. If the file does not exist yet, the clock is instead advanced to the modification time of
/usr/lib/clock\-epoch
\(en if it exists \(en or to a time derived from the source tree at build time\&. This mechanism is used to ensure that the system clock remains somewhat reasonably initialized and roughly monotonic across reboots, in case no battery\-buffered local RTC is available\&.
.sp
Added in version 219\&.
.RE
.PP
/usr/lib/clock\-epoch
.RS 4
The modification time ("mtime") of this file is used for advancing the system clock in case
/var/lib/systemd/timesync/clock
does not exist yet, see above\&.
.sp
Added in version 254\&.
.RE
.PP
/run/systemd/timesync/synchronized
.RS 4
A file that is touched on each successful synchronization, to assist
systemd\-time\-wait\-sync
and other applications to detecting synchronization with accurate reference clocks\&.
.sp
Added in version 239\&.
.RE
.SH "SEE ALSO"
.PP
\fBsystemd\fR(1),
\fBtimesyncd.conf\fR(5),
\fBsystemd.network\fR(5),
\fBsystemd-networkd.service\fR(8),
\fBsystemd-time-wait-sync.service\fR(8),
\fBsystemd.special\fR(7),
\fBtimedatectl\fR(1),
\fBlocaltime\fR(5),
\fBhwclock\fR(8)
